tunable parameters in simscape

Is there any possiblity to implement a tunable parameter within the simscape environment? I would need a tunable parameter such as seen in the simulink environments for a hydraulic pressure source. Thank you!

Answer 1

[Michelle Wu]

From your descriptions, it looks like Simscape run-time parameters might be something you are looking for. Simscape run-time parameters are coded as variables with values that you can change before or between simulations without recompiling the model. Please refer to the following link to learn more about what they are and how to use them:

https://www.mathworks.com/help/physmod/simscape/run-time-parameters.html

Please note that the above doc page is for the latest release R2017a. Depending on the release you currently use, the level of availability of such feature may also vary.

[Alicia Roder]

Thank you for your answer. I have already looked at run-time parameters. Unfortunately I need variables which can be changed during simulation not before or between simulations. But as far as I understand run-time parameters cannot be changed at runtime?

[Michelle Wu]

Unfortunately, you cannot change the value of a run-time configurable parameter during simulation. You can only change the value of a run-time configurable parameter when a simulation is stopped.

On the other hand, the value of a Simulink tunable parameter can be changed while a simulation is running. Because the Hydraulic Pressure Source can also take a signal from Simulink, it may be possible for you to use Simulink tunable parameter to suit your need depending on what kind of source you are looking for and what parameters you want to be tunable. Some parameters (like sample time and priority) are not tunable.

For example, if you would like a constant source for the Hydraulic Pressure Source, instead of using the "PS Constant" block from the Simscape Foundation Library, you may use a Simulink "Constant" block together with a "Simulink-PS Converter" block. Now you should be able to make this Simulink "Constant" block tunable for your application. Please refer to the following doc page for more information:

https://www.mathworks.com/help/simulink/ug/using-tunable-parameters.html

[Alicia Roder]

Thank you. I have investigated this model using a simulink constant and a Simulink-PS Converter. However it seems like this is just shifting the variable change to another place. Since the parameter in the pressure source depends on the changing variable, I again get an error message, stating I am changing a "state variable in a control loop" and the Simulation will not execute. I am suspecting that the feedback loop in Simscape might be part of the problem but Stateflow should offer the possiblity to react on physical parameters of the system?

[Alicia Roder]

Solved the problem by adding a memory block within the loop and replacing the constant pressure source with a fixed displacement pump. The fixed displacement pump can react on PS converted signals given out by stateflow. The Memory block adds an delay which makes it possible to solve the loop equations.

[Giovanni]

do not use memory block into loops! use dynamic blocks instead modeling, for example, the dynamics of a measure